Process for the manufacture of reconstituted tobacco foil



United States Patent l 3,310,058 PROCES FOR THE MANUFACTURE OFRECQNSTITUTED TOBACCO FOIL Albert B. Savage, Midland, and Juiius C.Aldrich, Mount Pleasant, Mich, assignors to The Dow Chemical Company,Midland, Mich, a corporation of Delaware No Drawing. Filed Apr. 20,1964, Ser. No. 361,221 Claims. (Cl. 131--17) This invention relates tothe manufacture of coherent tobacco foil containing a high percentage oftobacco and suitable as a binder for cigars, cigarillos, and similartobacco products. More particularly it relates to a selfsupportingreconstituted tobacco sheet of ground tobacco and an alkali-solublemethyl cellulose.

Numerous methods have been suggested for preparing reconstituted tobaccofoils from finely divided or pulverized tobacco particles unsuitable fordirect use in tobacco products. Such reconstituted foils must meet thegeneral test of acceptability in taste and burning characteristics aswell as having adequate physical properties such as tensile strength,dimensional stability and moisture retention. Furthermore, it is mostdesirable commercially to avoid use of an organic solvent system tominimize fire, explosion and toxicity hazards.

In United States Patent 3,025,860 Grossteinbeck and Holtz describe amethod for preparing tobacco foils by intilnately mixing finely dividedtobacco With a liquid binder and thereafter extruding the mixture into aprecipitating bath to solidify the binder and form the tobacco foil.Such cellulose derivatives as methyl cellulose, acetyl cellulose,carboxymethyl cellulose and ethyl cellulose are disclosed asparticularly suitable binders when dissolved in a suitable solvent suchas water, methylene chloride, acetone or a lower alcohol. With organicsolvents water is recommended as the precipitating agent, while foraqueous binder solutions water-miscible precipitants such as sulfuricacid, glycerol, glycol or sorbitol are recommended.

The present invention concerns a process for preparing a reconstitutedtobacco foil using alkali-soluble methyl cellulose as the binder. Theprocess comprises (A) preparing a tobacco slurry by intermixing finelydivided tobacco with an alkaline solution of alkali-soluble methylcellulose, (B) forming a thin stream of the tobacco slurry and treatingit with an aqueous inorganic acid-salt solution to coagulate the binderand form a self-supporting film, and (C) drying the film.

In the process the composition of the coagulation bath is an essentialfeature. The inorganic acid neutralizes the tobacco slurry while theinorganic salt causes coagulation and dehydration of the resultinginsoluble methyl cellulose binder. The coagulated tobacco film hassufficient wet strength so that it is easily transferred through theprocess baths.

When dried the reconstituted tobacco foil or sheet is flexible over awide range of temperature and humidity. Because of its appreciable wetstrength, it has reduced sensitivity to humidity changes. As a furtheradvantage of the present process, it has been noted that nicotine can beextracted from the tobacco during the processing and that withappropriate reagent concentrations and contact times the residualnicotine content of the reconstituted tobacco foil can be controlled.

In the practice of the present invention an alkali-soluble methylcellulose is employed as the tobacco binder. These methyl celluloseethers are insoluble in water and organic solvents but soluble in 2 to 8percent aqueous sodium or potassium hydroxide. They are lightlysubstituted ethers having a methoxyl content of about 5 to 13 weightpercent corresponding to a degree of substitution (D.S.) ranging fromabout 0.2 to 0.7. Particularly suit- 3,310,058 Patented Mar. 21, 1967ice vable is the alkali-soluble methyl cellulose described by Maasbergin United States Patent 2,408,326.

To obtain adequate blending it is necessary that the final slurry ofalkali-soluble methyl cellulose and tobacco have a maximum viscosity ofabout 5,000 cps. at 20 C. Conveniently a 5 to 8 percent solution of analkali-soluble methyl cellulose having a 2 percent viscosity of about15-100 cps. at 20 C. is used. For optimum results it is usuallydesirable to filter the alkaline methyl cellulose solution to removeinsoluble gels prior to addition of the tobacco. v

Any finely divided tobacco maybe employed. Tobacco chips, stems,clippings, and dust as well as other tobacco remains from normalmanufacturing processes can be pulverized or ground into a suitableform. Preferably the tobacco should be fine enough to pass through astandard 20 mesh screen. A finer grind gives a more homogeneous andsmoother appearance to the reconstituted foil.

To obtain a self-supporting reconstituted tobacco foil it is necessaryto use from about 15 to 50 parts of alkalisoluble methyl cellulose perparts of tobacco. While greater amounts of binder can be used, bettersmoking quality is obtained, of course, with a minimum of binder. Ifdesired, other conventional additives such as plasticizers, combustioncatalysts or retardants, hurnectants, can be added with the tobacco ormethyl cellulose or directly to the tobacco-methyl cellulose slurry.Thorough blending is accomplished with conventional equipment. Heatingthe slurry above about 30 C. should be avoided to minimize discolorationof the tobacco.

To form the reconstituted tobacco foil, the binder slurry is preferablyextruded into a coagulating bath through a die having a slit of properdimensions to obtain a dried reconstituted foil about 1.2 to 8 milsthick and of the desired width. Alternately it may be extruded or castonto a suitable surface such as a continuous belt and conveyed into thebath. The coagulant solution is preferably dilute sulfuric acidsaturated with sodium sulfate. As the caustic in the extruded slurry isneutralized by the acid, the sodium sulfate causes immediate coagulationand gela-tion of the water-insoluble methyl cellulose binder therebyforming a self-supporting film which can be drawn from the bath, waterwashed, dried and stored for use in the manufacture of tobacco products.

The inorganic acid-salt bath used to treat the extruded film serves notonly to convert the alkali-soluble'methyl cellulose into awater-insoluble form but also dehydrates and salts out the methylcellulose film. Since sulfates are particularly effective in salting outthe methyl cellulose film the sulfuric acid-sodium sulfate bath ispreferred. However, baths containing hydrochloric or phosphoric acid andthe corresponding salts can also be used. For rapid neutralization withthe preferred sulfuric acid bath, the concentration of sulfuric acidshould be at least 8 percent and preferably from about 10 to 30 percent.The sodium sulfate content should be at least 15 percent and preferablynear the saturation level. By addition of make-up sulfuric acid andwater and removal of spent coagulation solution, the concentration ofacid and salt can be maintained within desired limits for continuousoperation. Bath temperatures of from about 15 to 45 C. can be employed,but since rapid coagulation is enhanced by heat, a temperature between30 and 45 C. is often advantageous. Higher temperatures tend to degradethe tobacco foil.

To achieve essentially complete neutralization and coagulation of atobacco film up to about 10 mils thick, a contact time in the sulfuricacid-sodium sulfate bath of from about 10 to 60 seconds at 30 to 40 C.is usually adequate. The reconstituted tobacco foil is then taken fromthe coagulation bath and washed with water to re- 3 move the excess acidand the soluble salts. The water wash can be accomplished using a waterbath, water sprays, or other means, but preferably with water preheatedto between 40 and 95 C. since hot water is more effective in removingthe salts and strengthening the coagulated film.

Following the water wash the reconstituted tobacco foil can be furthertreated as desired prior to final drying. For example, brief contactwith a dilute sodium bicarbonate solution can be used to insure completeneutralization of any residual inorganic acid. Further water washing canbe used to reduce the nicotine content. A foil weakened by prolongedsoaking in water can be strengthened by return to the acid-salt bath.Finally the tobacco foil can be plasticized with a humectant if desiredby dipping in 5 to 15 percent aqueous propylene glycol or glycerine justprior to drying.

The reconstituted tobacco foil is dried at 20 to 120 C. advantageouslythrough contact with a heated metal roll having a surface temperature offrom about 100-120 C. To minimize darkening of the tobacco foil,temperatures higher than about 120 C. should be avoided.

In this process a reconstituted tobacco foil having a dried thickness ofat least 1.2 mils has adequate strength even in the coagulation bath sothat it is self-supporting under normal operating conditions. However,for high speed operations, use of a continuous belt or similar means tosupport the foil may be advantageous.

The dried reconstituted tobacco foil containing alkalisoluble methylcellulose as a binder is flexible and selfsupporting over a wide rangeof temperature and relative humidity. Typically it contains by analysisless than 0.5 percent organic acid calculated as sulfuric acid and lessthan 0.1 percent inorganic sulfate. It is readily wound into coils whichcan be stored under ambient conditions although storage at a relativehumidity of from about 20 to 80 percent is preferred for optimum qumity.This reconstituted foil has enhanced resistance to moisture and suitabletensile strength and dimensional stability for use as a binder in thepreparation of tobacco products.

This invention is further illustrated by the following representativeembodiment. Unless otherwise specified, all parts and percentages are byweight.

To a solution of 90 parts of sodium hydroxide in 800 parts of water wasadded 5 3 parts of alkali-soluble methyl cellulose (6.0% -OCH having aviscosity of 72 cps. as a 2% solution in 6% caustic at 20 C., 4 parts ofa liquid polyoxyethylene glycol (M.W. 200) and 4 parts of a solidpolyoxyethylene glycol (M.W. 4,000). The mixture was stirred thoroughlywhile cooling to about to C., filtered through a 150 mesh screen toremove insoluble particles and deaerated by centrifuging. Then a slurryof 159 parts of finely divided tobacco (100 mesh) and 610 parts of waterwas added to the alkaline methyl cellulose solution. The binder andtobacco slurry was thoroughly intermixed, deaired and then transferredto the reservoir of a film extrusion die having a 0.014" x 5.0" slit.

The die was positioned at one end of a sulfuric acidsodium sulfate bathwith the slit adjusted horizontally below the surface of the coagulantsolution. The solution contained by analysis 12.9% sulfuric acid and20.3% sodium sulfate and was held in a nickel trough 4.5 wide, 48" long,with a bath depth of about 2". The bath temperature was about 28 C. Bymeans of air pressure on the reservoir, the slurry was extruded into thebath as a stream which instantly coagulated to a continuous film. Thecoagulated film was withdrawn at the opposite end of the bath after atotal immersion time of about 30 seconds using a 2.5 diameter plasticroll having a surface speed of 8 ft./min. It was then rinsed in a bathof flowing hot water (60-65 C.) for about 30 seconds and woundcontinuously on a drum driven by .a slip clutrh.

A portion of this reconstituted film was further treated by immersion ina 1.2% sodium bicarbonate solution for 10 seconds followed by rewashingin the hot rinse bath and finally by immersing in a solution of 10%aqueous glycerol for about 1 to 3 seconds. Several samples of theplasticized film were dried on glass plates overnight at roomtemperature and 50% relative humidity. The remainder was dried on aninfrared heated polished metal cylinder having a surface temperature ofabout to C. with a contact time of 2 minutes. Darkening occurred athigher temperatures. The dried tobacco film had a thickness of 3 to 4mils, was flexible, moisture resistant and easily coiled.

Film samples taken at several stages were analyzed for sulfuric acid andsodium sulfate content by repeated extraction with hot water andanalysis of the aqueous extract by standard methods. Typical analysesare given in Table 1.

a Parts per part of dried extracted foil. b Includes water-solubleplasticizers.

Using a standard Instron test machine, the dry strength of theplasticized tobacco foil having a film thickness of from 3 to 4 mils was400-700 p.s.i. The wet strength of the foil was determined using a ScottIP-2 Serigraph and a 1 x 2" strip of foil, the load being applied oneminute after wetting the foil. For foils about 3 mils thick typical wetstrengths ranged from 100 to 200 =g./ in. width and for foil about 4mils thick, from 200-300 g./-in. width.

In other similar runs the extruded tobacco-alkalisoluble methylcellulose slurry was neutralized and coagulated with dilute hydrochloricacid saturated with sodium chloride and with dilute phosphoric acidsaturated with sodium phosphate. Satisfactory reconstituted tobacco foilwas obtained.

We claim:

1. A method of producing a reconstituted tobacco foil comprising:

(A) Preparing a tobacco slurry by intermixing 100 parts of finelydivided tobacco with an alkaline solution containing from 15 to 50 partsof alkalisoluble methyl cellulose having a D.S. of about 0.2 to 0.7,said slurry having a viscosity of less than about 5,000 cps. at 20 C.;

(B) Forming a thin stream of the tobacco slurry and treating it with anaqueous inorganic acid-salt coagulated bath selected from the groupconsisting of aqueous sulfuric acid and sodium sulfate, aqueoushydrochloric acid and sodium chloride, and aqueous phosphoric acid andsodium phosphate whereby it is coagulated into a self-supporing film;and

(C) Drying the film.

2. The method of claim 1 wherein the alkali-soluble methyl cellulose hasa viscosity of from about 15 to 100 cps. as a 2 percent solution indilute caustic at 20 C.

3. The method of claim 1 wherein the tobacco slurry is extruded into thecoagulating'bath.

4. The method of claim 1 wherein a coagulant bath of sulfuric acid andsodium sulfate is employed.

5. The method of claim 1 wherein a coagulant bath of hydrochloric acidand sodium chloride is employed.

6. The method of claim 1 wherein a coagulant bath of phosphoric acid andsodium phosphate is employed.

7. The method of claim 4 wherein the bath contains .at least 8 weightpercent of sulfuric acid and Weight percent of sodium sulfate.

8. A reconstituted tobacco foil comprising finely divided tobacco and aminor proportion of alkali-soluble methyl cellulose characterized by adegree of substitution of from about 0.2 to 0.7 and a viscosity of fromabout 15 to 100 cps. as a 2 percent solution in dilute caustic at C.

9. The reconstituted tobacco foil of claim 8 containing from about 15 toparts of alkali-soluble methyl cellulose per parts of finely dividedtobacco.

10. The method of claim 4 wherein the tobacco slurry is coagulated in abath containing from 10-30 weight References Cited by the ExaminerUNITED STATES PATENTS 3/1951 Cox 264187 3/1962 Grossteinbeck et a1.131-140 10 SAMUEL KOREN, Primary Examiner.

MELVIN D. REIN, Examiner.

8. A RECONSTITUTED TOBACCO FOIL COMPRISING FINELY DIVIDED TOBACCO AND A MINOR PROPORTION OF ALKALI-SOLUBLE METHYL CELLULOSE CHARACTERIZED BY A DEGREE OF SUBSTITUTION OF FROM ABOUT 0.2 TO 0.7 AND A VISCOSITY OF FROM ABOUT 15 TO 100 CPS. AS A 2 PERCENT SOLUTION IN DILUTE CAUSTIC AT 20*C. 